The present invention relates to a discharge lamp, where luminescent substances are sealed in an arc tube that is mainly made of, for example, a translucent ceramic, as well as to a method of sealing such a discharge lamp and an apparatus for sealing such a discharge lamp.
In these discharge lamps, an electrode member having a pair of electrodes is fixed in an air-tight manner to an opening of an arc tube, which is mainly made of a translucent ceramic, and luminescent substances, such as mercury, inert gases, and metal halides, are sealed in the air-tight manner in the arc tube. In such discharge lamps, a known method applied to seal the opening of the arc tube in the air-tight manner fuses a sealing glass like a glass frit and seals a gap between the electrode member and the opening of the arc tube with the fused sealing glass.
One known technique uses infrared radiation as a heat source for fusing the sealing glass. When a residual part of the arc tube other than the sealing glass is irradiated with infrared emission, the luminescent substances fly out of the arc tube. The technique can not accordingly attain the desired properties of the discharge lamp.
The object of the present invention is thus to provide a discharge lamp that reduces a fly loss of luminescent substances in an arc tube in the process of sealing an opening of the arc tube by using infrared radiation, as well as a method of sealing such a discharge lamp, and an apparatus for sealing such a discharge lamp.
A first application of the present invention is directed to an apparatus for sealing a discharge lamp, which fuses a sealing glass to seal an opening of an arc tube, through which a luminescent substance has been charged into the arc tube. The apparatus includes: a support jig that supports the arc tube, which is provided with the sealing glass placed around a circumference of the opening; and an infrared irradiation unit that emits infrared radiation to fuse the sealing glass, wherein the support jig is mainly made of a material that has a greater thermal conductivity than that of the arc tube.
The apparatus for sealing a discharge lamp in accordance with the first application of the present invention seals the opening of the arc tube, through which the luminescent substances are charged into the arc tube, by fusing the sealing glass with heat of infrared radiation emitted from the infrared irradiation unit. One end of the arc tube is supported by the support jig. The support jig is mainly made of a material having a greater thermal conductivity than that of the material of the arc tube, for example, a metal material like Al or Cu. This enables heat to be readily conducted from the arc tube to the support jig and thereby prevents a temperature rise in the arc tube. This arrangement effectively prevents the luminescent substances from being vaporized and released from the arc tube.
A cooling unit that lowers the temperature of the support jig is favorably provided to enhance the heat conduction from the arc tube to the support jig.
In accordance with one preferable embodiment of the first application, the apparatus for sealing a discharge lamp further includes an infrared shield that restricts the infrared radiation emitted from the infrared irradiation unit to a periphery of the sealing glass. This structure enables only the sealing glass to be fused for sealing the opening, while shielding the other part of the arc tube from the infrared radiation. This accordingly prevents a temperature rise in the arc tube.
In accordance with one preferable arrangement, the support jig is attached to the infrared shield via a heat-insulator. This arrangement simplifies the attachment structure of the infrared shield. The heat-insulator reduces the quantity of heat conducted from the infrared shield to the support jig. This arrangement accordingly decreases the quantity of heat conducted from the support jig to the arc tube and prevents a temperature rise in the arc tube.
A second application of the present invention is directed to a method of sealing a discharge lamp. The method fuses a sealing glass to seal an opening of an arc tube, through which a luminescent substance has been charged into the arc tube. The method includes the steps of: supporting one end of the arc tube with a support jig; placing the sealing glass around a circumference of the opening; and irradiating the sealing glass with infrared emission to fuse the sealing glass and thereby seal the opening, and cooling the support jig.
The method of sealing a discharge lamp given as the second application cools the support jig down in the course of fusing the sealing glass placed on the arc tube, while the arc tube is supported by the support jig. This arrangement enhances the heat conduction from the arc tube to the support jig and thereby prevents a temperature rise in the arc tube.
A third application of the present invention is directed to an apparatus for sealing a discharge lamp, which fuses a sealing glass to seal an opening of an arc tube, through which a luminescent substance has been charged into the arc tube. The apparatus includes: a support jig that supports one end of the arc tube; a feeding conduit that is arranged to cover the arc tube in an air-tight condition; an infrared irradiation unit; and a heating unit that condenses infrared radiation emitted from the infrared irradiation unit on a predetermined light condensing area, in order to fuse the sealing glass placed around a circumference of the opening of the arc tube. The heating unit has an opening, through which one end of the feeding conduit is protruded outward.
In the third application of the present invention, the opening of the heating unit enables the user to monitor the state in the heating unit. When a part of the feeding conduit is stained, the other end of the feeding conduit that is not projected from the opening is cut off. This shifts the position of the stained part of the feeding conduit relative to the light condensing area of the infrared radiation and thereby favorably avoids frequent replacement with a new feeding conduit.
It is preferable that the heating unit has a transparent window, through which the user can observe the state of fusing the sealing glass and sealing the opening of the arc tube. This arrangement enables the user to securely check the state of sealing the opening with the fused sealing glass.
In accordance with one preferable embodiment of the third application, the heating unit has: a flow length detection unit that measures a flow length of the fused sealing glass flown into the arc tube; and a heating control unit that stops the emission of the infrared irradiation unit when the flow length of the fused sealing glass measured by the flow length detection unit becomes not less than a predetermined value. This arrangement ensures the accurate detection of the flow length of the sealing glass and attains automation without requiring the process of monitoring the sealing state.
A fourth application of the present invention is directed to a discharge lamp, which includes: an arc tube with an opening; an electrode member that is inserted into the arc tube through the opening and has an electrode element; and a halide sealed in the arc tube, wherein electricity is suppled to the electrode member to make the halide radiate. The electrode member has a film layer on a circumference thereof. The film layer includes: a thin film layer that is formed on a specific part, which is in contact with the halide in the arc tube, and includes a halide-resistant material having high corrosion resistance to the halide; and a buffer layer that is interposed between the thin film layer and the circumference of the electrode member and formed to have a medium thermal expansion coefficient, which is between a thermal expansion coefficient of the thin film layer and a thermal expansion coefficient of the electrode member.
In the discharge lamp given as the fourth application, the film layer including the thin film layer and the buffer layer is formed on the electrode member. Since the thin film layer having the resistance to the halide is formed on the specific part that is in contact with the halide, the electrode member has high corrosion resistance to the halide-containing luminescent substances and thereby excellent durability.
The buffer layer is interposed between the electrode member and the thin film layer and has a thermal expansion coefficient, which is between the thermal expansion coefficient of the material of the electrode member and the thermal expansion coefficient of the material of the thin film layer. Even if the discharge lamp is exposed to the heat cycle from ordinary temperature to the emission temperature of the discharge lamp, this configuration reduces the thermal stresses on these interfaces and effectively prevents the thin film layer from coming off the electrode member.
In accordance with one preferable embodiment, the buffer layer contains both the halide-resistant material and a material of the electrode member. The buffer layer has concentration of the halide-resistant material that continuously increases from the electrode member towards the thin film layer.
A fifth application of the present invention is directed to a method of manufacturing a discharge lamp. The method inserts an electrode member into an arc tube through an opening thereof and gives electricity to the electrode material, so as to make a halide, which is sealed in the arc tube, radiate. The method includes the steps of: providing the electrode member; forming a buffer layer, which partly contains a halide-resistant material, on surface of the electrode member; and forming a thin film layer, which comprises the halide-resistant material, around a circumference of the buffer layer.
One preferable method applicable for forming the thin film layer and the buffer layer exposes the electrode member to a halide-resistant material-containing vapor. This attains a continuous increase in concentration of the halide-resistant material included in the buffer layer and causes the thin film layer to be formed on the buffer layer. Typical examples of the halide-resistant material include metals and allows of W, Mo, Zr, and Re.
A sixth application of the present invention is directed to a discharge lamp, which includes: an arc tube having a large-diametral portion that has a hollow chamber filled with a luminescent substance and a small-diametral portion that extends from the large-diametral portion and defines a narrow tubular chamber, which is continuous with the hollow chamber; an electrode member having a sealing base element that is fitted in an opening of the small-diametral portion, a lead element that is arranged to run from the sealing base element to the hollow chamber and to be apart from an inner wall face of the small-diametral portion by a predetermined space, and an electrode element that is disposed on a free end of the lead element; and a sealing glass that is interposed between the inner wall face of the small-diametral portion and an outer surface of the sealing base element, in order to seal the hollow chamber and thereby disconnect the hollow chamber from outside of the arc tube. A length of the lead element is determined to cause a temperature of a specific part of the sealing glass that is exposed to the hollow chamber to be lower than a glass transition temperature, at which the sealing glass is softened, at least at a time of emission of the discharge lamp.
In the discharge lamp given as the sixth application, the arc tube has the large-diametral portion and the small-diametral portion. The large-diametral portion has a hollow chamber, in which luminescent substances are sealed. The hollow chamber is continuous with a narrow tubular chamber defined by the small-diametral portion. The opening of the small-diametral portion is sealed with the sealing base element formed on one end of the electrode member via the sealing glass. The lead element extending from the sealing base element runs through the narrow tubular chamber to the hollow chamber and has the electrode member on the free end thereof. Electricity given to the electrode member having this configuration causes arc discharge and makes the luminescent substances volatile for discharge emission.
At the time of emission of the discharge lamp, the discharge emission raises the temperature in the hollow chamber and causes the thermal energy to be conducted to the sealing glass via the narrow tubular chamber. The length of the lead element is determined to cause the temperature of the specific part of the sealing glass that is exposed to the hollow chamber to be lower than the glass transition temperature. The temperature of the specific part of the sealing glass that is exposed to the hollow chamber is accordingly kept to be not greater than the glass transition temperature, irrespective of the temperature of the luminescent substances and the state of liquid phase and solid phase. This arrangement effectively prevents deterioration of the sealing glass.
In the event that the sealing glass used for the discharge lamp is in a temperature range that is higher than the glass transition temperature, the constituents of the sealing glass are freed from the sealing glass to cause a spectra of the constituents other than the expected spectra of the discharge lamp or to change the intensity of the spectra. This adversely affects the properties of the discharge lamp. In the discharge lamp according to the sixth application of the present invention, however, the sealing glass is kept at lower temperatures than the glass transition temperature and is thus free from such adverse effects.
A seventh application of the present invention is directed to a discharge lamp, which includes: an arc tube that is mainly made of a translucent material and comprises a large-diametral portion, which has a hollow chamber filled with a luminescent substance, and a small-diametral portion, which extends from the large-diametral portion; and an electrode member that is arranged to run from an opening of the small-diametral portion to the hollow chamber and has on a free end thereof an electrode element, which is placed inside the hollow chamber. Electricity is given to the electrode member to cause arc discharge and thereby attain emission of the discharge lamp. The large-diametral portion is formed to cause a temperature of a substantially whole wall surface facing the hollow chamber at a time of the emission of the discharge lamp to be substantially equal to a heat-resistant temperature of the translucent material.
In the discharge lamp given as the seventh application, the large-diametral portion of the arc tube is formed to cause the temperature of the substantially whole wall surface facing the hollow chamber at the time of the emission of the discharge lamp to be substantially equal to the heat-resistant temperature of the translucent material. This arrangement prevents thermal deterioration of the arc tube and heightens the arc temperature in the hollow chamber, thereby improving the emission efficiency.
It is preferable that the arc tube is mainly made of the translucent material having a thermal conductivity of not smaller than 0.9 cal/cmxc2x7sxc2x7xc2x0 K. The arc tube is designed to raise the temperature of a coolest part in the small-diametral portion as high as possible at the time of the emission by heat conduction from the large-diametral portion to the small-diametral portion. The large thermal conductivity of the arc tube exerts the following effects. The occurrence of arc discharge on the electrode element of the discharge lamp increases the temperature in the arc tube. The heat is conducted from the large-diametral portion to the small-diametral portion in the arc tube and further from the small-diametral portion to the electrode member, and is released from the electrode member. The large thermal conductivity of the arc tube enables the heat in the large-diametral portion to be quickly conducted to the small-diametral portion and thereby increase the temperature in the small-diametral portion. The luminescent substances located in the coolest part of the small-diametral portion are affected by the temperature rise and improve the emission efficiency in the initial stage, thereby enhancing the total emission efficiency.
In an eighth application of the present invention, the small-diametral portion extending from the large-diametral portion has a low heat conduction part, which is made of a specific material having a lower thermal conductivity than a thermal conductivity of the large-diametral portion and functions to reduce heat conduction from the large-diametral portion to the sealing glass. Since part of the small-diametral portion forms the low heat conduction part having the lower thermal conductivity than the thermal conductivity of the large-diametral portion, this arrangement reduces the heat conduction from the large-diametral portion to the sealing glass via the small-diametral portion. The low heat conduction part reduces the quantity of heat conducted to the sealing glass, even if the arc tube has a high temperature. This arrangement effectively prevents the temperature of the sealing glass from exceeding the glass transition temperature. The whole small-diametral portion, instead of part of the small-diametral portion, may form the low heat conduction part. The location of the low heat conduction part is not restricted as long as it can contribute to a decrease in temperature of the sealing glass.
A tenth application of the present invention is directed to a method of sealing a discharge lamp. The method fuses a sealing glass to seal an opening of an arc tube, through which a luminescent substance has been charged into the arc tube. The method includes the steps of: setting the sealing glass around a circumference of the opening; fusing the sealing glass; and rapidly cooling down the fused sealing glass to make the sealing glass amorphous and thereby seal the opening.
In the method of sealing a discharge lamp given as the ninth application, the fused sealing glass is rapidly cooled down to be amorphous, in the process of sealing the opening of the arc tube with the sealing glass. This configuration enhances the durability to the heat cycle at the time of the emission of the discharge lamp.
In a ninth application of the present invention, the apparatus for sealing a discharge lamp further includes an infrared shield that is disposed around a circumference of the arc tube to condense the infrared radiation only on a periphery of the sealing glass and shield a residual part of the arc tube from the infrared radiation. The infrared shield enables only the periphery of the sealing glass to be heated, while protecting the residual part of the arc tube from heat and the resulting temperature rise. This arrangement thus prevents the luminescent substances from flying out of the arc tube.
It is preferable that one end of the arc tube is supported by a support jig and that an adsorbent is placed in the feeding conduit to adsorb impurities in the process of sealing the arc tube while the feeding conduit is set in the air tight condition. Even if there are impurities in the feeding conduit, the adsorbent adsorbs the impurities and thereby prevents contamination with the impurities, which may cause troubles in the arc tube.
It is also preferable that the support jig has a suspension jig that suspends the electrode member while one end of the arc tube is supported by the support jig. This structure prevents the electrode member from dropping in the arc tube in the course of fusing the sealing glass.
An eleventh application of the present invention is directed to a method of sealing a discharge lamp, The method irradiates a sealing glass with infrared emission to fuse the sealing glass and thereby seal an opening of an arc tube, through which an electrode member with an electrode element is inserted into the arc tube. The method includes the steps of: setting the sealing glass around a circumference of the opening; regulating an atmosphere to make a pressure in the arc tube lower than an external pressure and cause a pressure difference; and heating and fusing the sealing glass to make the fused sealing glass flown into a gap between the electrode member and a wall surface of the opening by mean of the pressure difference.
In the method of sealing a discharge lamp given as the eleventh application, the fused sealing glass is exposed to the pressure difference between the inside and the outside of the arc tube when being flown into the gap between the electrode member and the opening of the arc tube. This arrangement enables the fused sealing glass to be smoothly flown into even a very narrow gap. The flow length of the fused sealing glass is readily controlled by regulating the pressure difference.
One preferable embodiment of the sealing glass includes Al2O3xe2x80x94SiO2 as a primary constituent and further contains an infrared absorbent to enhance absorptance of infrared radiation. The infrared absorbent is at least one selected among the group consisting of CeO2, Sm2O3, Ho2O3, Dy2O3, Er2O3, and Nd2O3. The infrared-absorbing substance contained in, for example, a glass ring enables the infrared radiation to be condensed on the glass ring and rapidly increase the temperature of the glass ring, thereby ensuring completion of the sealing process within a short time period. The shortened heating time effectively restrains a temperature rise in the arc tube and prevents the luminescent substances from flying out of the arc tube. The infrared-absorbing substance may be mixed with a coating material, which is applied onto the surface of the glass ring, instead of being directly mixed with the primary constituent of the glass ring.